The principles governing the operation of the intricate neural circuits in the brainstem are enigmatic, despite their vital importance in the control of virtually every major homeostatic function in the body. In the brainstem, the nucleus tractus solitarius (NTS) and the dorsal motor nucleus of the vagus (DMV) are of paramount importance. The NTS processes afferent information from vast regions of the body, communicates with other brainstem and forebrain structures, and contains a myriad of neurotransmitters. The DMV is the primary channel through which the NTS sends parasympathetic signals out to the major organ systems. To gain insight into how these two nuclei integrate information representing diverse sensory modalities, this study will focus on the relationship between a subset of the afferents to NTS, those originating from the oral cavity, and a subset of the efferents from DMV, those directed to the subdiaphragmatic viscera. Oral sensory stimulation modulates a variety of gastrointestinal functions by activating the parasympathetic nervous system. These "cephalic phase reflexes" may be important for priming and optimizing digestive processes and nutrient metabolism. The central circuitry governing these reflexes has not been characterized. Understanding this circuitry is important in itself because of its potential involvement in disorders of digestive and metabolic functions. Oral sensory information ascends directly to rostral NTS, and modulates enteric functions through the DMV. The long term objective of this project is to characterize the connections linking rostral NTS to vagal motoneurons projecting to subdiaphragmatic viscera. These connections may contain the key to understanding how cephalic phase reflexes are organized and controlled by the brainstem. Specific aims are: (1) to locate vagal motoneurons activated either by oral sensory afferents in the solitary tract, or by rostral NTS neurons, and (2) to map the NTS presynaptic inputs to each of these neurons. Comparison of these maps will indicate if vagal output is under the control of discrete combinations of sensory inputs.